| Temperature is a very important factor affecting crop growth and development, so it isnecessary to provide crops with appropriate temperature condition in greenhouse production.In the traditional mode of production, northern greenhouse overwintering production is oftenneeded to increase the indoor temperature through the consumption of coal, oil and other nonrenewable resources. In the resource competition so intense today, energy conservation is thefirst choice, therefore the production and application of some cheap renewable resources havebecome the research focus of people. Phase change materials are just about some of the newand renewable resources which have the potential value in use. Through research and analysis,using the phase change material instead of the traditional greenhouse heating, effectivelyimprove the greenhouse thermal environment, which will have a very great meaning ongreenhouse production.In order to make the phase change thermal storage technology can be better used inthe greenhouse thermal insulation, in this paper, sodium sulfate decahydrate choose wasselected as the main phase change material, and physical blending method has been used tomodified the PCM, which wants to obtain high-quality phase change thermal storage systemmeeting the requirement of greenhouse crop production, to effectively improve thegreenhouse thermal environment, reduce energy consumption and pollution. The effect ofvarious additives, the content of nucleating agent and the reaction temperature have beenexplored, we have got its optimal ratio and analyzed the thermal stability by melting coolingcycle, DSC, FTIR test etc. The experimental results show that, by adding the10%meltingtemperature regulator KCl,3%of the nucleating agent borax,2%of thickeningagent PAM and0.1%crystallization modifier SHMP preparing the Na2SO4·10H2O phasechange heat storage system, whose freezing point is20.5℃, the melting point is23.77℃andthe melting enthalpy is129.1J/g. Through the FTIR test and200melting cooling cycle test,we found that the phase change thermal storage system has good thermal stability, it meansthat the addition of exogenous substance did not change the material component ofNa2SO4·10H2O.According to the common brick wall heat releasing at night to determine the usageamount of phase change thermal storage system, through calculation, when the dosage is18.4kg/square meters, its heat releasing amount is equal with that of traditional wall which wall structure is the240mm brick+100mm polystyrene board+240mm brick at roomtemperature for8℃.In order to verify the effect of application of phase change thermal storage system in thegreenhouse, putting Na2SO4·10H2O phase change heat storage system into the box whichspecifications is600mm×450mm×50mm, and placed them in the front of the wall of thegreenhouse and the effect of its application in the greenhouse was studied in the end. Theanalysis results of the thermal environment in greenhouse shows that the lowest temperatureof trial greenhouse was gradually increased after the plastic box was installation. At first thenight temperature in trial greenhouse was0.9℃lower than the control and the later it can be2.0℃higher than the control; the difference of their day temperatures and relative humiditywere not obvious before and after the installation of the phase change material box. The20cmground temperature of trial greenhouse was2.0℃higher than the control. The accumulatedheat release of phase change material box during cloudy night is1.10MJ/㎡, higher thanaccumulated heat on the daytime which is1.07MJ/㎡. While the accumulated heat release ofbrick wall and phase transition block wall are1.01MJ/㎡and0.51MJ/㎡respectively. All ofthis indicates that the application effect of phase change materials box in the greenhouse isrelatively good, which has a good application respect. |
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